The present invention is directed, in general, to a method of testing an unknown sample with an analytical tool and, more specifically, a method of testing an unknown sample with an analytical tool specifically chosen, after determining the detection limit and calibration associated with the tool, for a particular matrix.
In semiconductor processing today, it is often necessary to spectroscopically examine portions of a semiconductor die to determine the results of new or conventional processes. The examination may be to confirm the results of an experimental process, to determine the nature of a particular failure or defect in a semiconductor device, or even to find impurities within the semiconductor device. Of course, because of the nature of integrated circuits, the examination must often be performed on samples cut from the die in question. Scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) is frequently used in the determination of the composition of target materials in a feature of a semiconductor die. Other analytical tools are also available to examine these samples, for example a few are auger electron spectrometer (AES), secondary ion mass spectrometer (SIMS), and transmission electron microscope (TEM).
Often, a semiconductor die or wafer is taken off the production line and brought to one of the analytical tools discussed above, to look for impurities. This is a very important step in semiconductor manufacturing because certain impurities, in certain concentrations and within specific materials, typically cause semiconductor device failure. Since it is commonly known which impurities are not desired within a specific material, and since the impurity concentration that is unacceptable is also known, the analytical tools can often be of help.
Certain analytical tools are more helpful, when looking for certain impurities in specific concentrations. Currently, certain analytical tools are known for being better suitable for different applications; however, each tool""s detection limit, for a given element within a given material, today may only be approximated and not known within an acceptable degree of certainty. This impacts the semiconductor manufacturing industry, in that a person performing a test on a semiconductor wafer cannot say, with great certainty, that even though the element did not register, less than X amount must be present. Moreover, the various detection limits of the different analytical tools are not known with enough certainty, that a given impurity scenario could be allocated to a certain tool.
Accordingly, what is needed in the art is a calibration method for use in analytical inspection tools, that allows the analytical tools to have a detection limit associated therewith depending on the impurity desired, concentration thereof and material located within, that alleviates the problems associated with the prior art.
To address the above-discussed deficiencies of the prior art, the present invention provides a method of testing an unknown sample with an analytical tool. The method, in a illustrative embodiment, includes calibrating an analytical tool to a calibration standard having a known concentration of an element therein and obtained with a focused beam, thereby to achieve a calibrated analytical tool, determining an unknown concentration of the element within the unknown sample with the calibrated analytical tool, and correcting the unknown concentration with the calibration standard.